The disclosure relates generally to inks, for example, solid inkjet inks. More specifically, the disclosure relates to pigment resinous compounds particularly compatible with or useful as compositions useful in stabilizing pigment particles in solid inks at high temperatures. In embodiments, the pigment resinous compounds comprise a long chain having at least 10 carbon atoms for stabilizing pigment particles in solid inks, and further comprise amines for adsorbing onto the pigment particle surface.
Pigments generally offer better colorfastness over dyes, and are characterized by low specific gravity and greater resistance to migration than dyes. In addition, pigment-based inks are more robust than dye-based inks, and are relatively much less expensive than dye colorants, especially custom dye colorants. However, many of the solid ink jet ink compositions contain dye colorants instead of pigment colorants, because it is difficult to overcome the challenges in developing pigment-based inks. The challenges include properly dispersing the pigment particles in the ink and being able to reliably jet the ink without clogging the printheads by the pigment particles.
Pigments are known to be hard to disperse in most media because they tend to aggregate in large structures. In addition, print-heads are typically operated at high temperatures, for example, from 115° C. to 120° C., which has a destabilizing influence on the pigment dispersion.
Many of the commercially available polymeric dispersants are designed for aqueous based or solvent based inks, and therefore, they are not compatible with the hydrophobic wax based solid inks. Further, these polymeric dispersants are in liquid or paste forms, thus they cannot withstand the excessive temperatures in the printer for long periods of time. Lastly, the use of polymers in solid ink is not favored because: a) polymers have a negative impact on rheological properties producing non-newtonian behavior which cause viscosity to increase, b) polymers tend to form filaments which affect drop formation of the ink during jetting (i.e. the formation of small drop sizes of the ink).
Thus, there exists a need for pigment stabilizing resinous compounds that are chemically stable, are compatible with the solid ink formulation, and are capable of effectively dispersing and stabilizing pigment particles in solid inks over long periods of time at high temperatures.
In order to solve the above-identified problems, this disclosure describes pigment stabilizing resinous compounds that are capable of providing steric stabilization of the pigment particles in solid ink, and being able to be adsorbed (or anchored) to the pigment particle surface.
FIG. 1 illustrates a pigment stabilizing resinous compound 2 being anchored onto a pigment particle 1. The pigment stabilizing resinous compound (or resinous compouns, or tri-component resins) 2 comprises a waxy chain that contains two components (i.e. a hydrocarbon or polymeric long chain at the tail end of the molecule, and a chain extensor at the middle part of the molecule) known as a brush or a stabilizing tail, for providing steric stabilization of the pigment particles in solid ink, or for being compatible with the non-polar wax based solid ink. Because longer stabilizing tails improve stabilization of pigments in solid ink, the chain extensor helps to increase the length of the waxy chain. For solid inks composed mainly of polyethylene wax, therefore in some embodiments, a suitable brush would be polyethylene wax based, and the like, although other materials can also be used for the brush. The pigment stabilizing resinous compound (or resinous compouns or tri-component resins) 2 further comprises functional groups 5, which includes but are not limited to various amines, that can strongly adsorb (or anchor) onto the pigment particles surface through hydrogen bonding to provide pigment stabilization, so that the pigments can withstand high temperatures (>100° C.) used in most solid ink printers. In some instances regarding pigment particle stabilization of inks and the like, it can be advantageous to have the pigment particles stabilized through adsorption of the stabilizing resinous compound 2 onto the pigment particle 1 such that the functional groups 5 of the stabilizing resinous compound 2 are anchored onto the pigment. The waxy chain 3 and/or 4 of the stabilizing resinous compound 2 are optimally selected for both its molecular weight and its miscibility with the ink carrier in such a way that the stabilizing resinous compound provides an effective steric barrier that hinders pigment particle flocculation.